This invention relates to a recording and reproducing apparatus utilizing electron beams, and more particularly to an electron beam apparatus suitable for writing and reading high density digital signals.
Various proposals have been made in the past on recording apparatuses utilizing an electron beam. The greatest advantage brought forth by the utilization of the electron beam lies in high density recording which makes it possible to effect recording in a unit smaller than the wavelength of light by fine electron beams. In practice, however, the scale of the apparatus becomes extremely great in order to finely converge and deflect the electron beam and to accomplish high density recording or reproduction. In other words, even if high density integration of memory devices is attained, there would be no merit if the apparatus itself using them remains great in size. To solve this problem, an attempt has been made to seal the recording device and the convergent electron beam system into an electron tube as described, for example, in G.E. R&D Review, 1977, p 12-15. In this case, too, the recording density as viewed from the user's side is one that is averaged by the overall capacity of the tube.
Another proposal is described in Japanese Patent Laid-Open No. 221846/1984. This prior art is based upon the concept of a conventional magnetic or optical disc device and enlarges the scale of an apparatus constituting the convergent electron beam system and enlarges the recording device itself, too. A disc is rotated in vacuum and the fine electron beam is deflected for recording and reproduction. The electro-optical system used in this prior art is equivalent to an electron beam lithography system used for fine-patterning of semiconductors, or the like. In other words, the electron beam is converged (a) as finely as possible after obtaining a necessary current for exposure and scans it (b) as quickly as possible and (c) over area as wide as possible at a certain constant position on a mechanical sample moving device.
Therefore, even if the electron beam can be easily converged to about 100 .ANG. as in a scanning electron microscope, recording and reproduction would require several hundreds of hours of time if the conditions (b) and (c) are not taken into consideration. In order for the recording by electron beam to be obviously superior to the recording density by light, a recording area of about 0.1 .mu.m per bit must be secured, and in this point, the prior art method described above involves a critical problem. Suppose an electron beam having a diameter of 0.1 .mu.m is deflected by a final convergent(objective) lens having a focal distance of 10 to 20 cm in the electron beam lithography system described above, the deflection quantity on the sample surface is up to 10 mm due to the aberration blur that occurs due to deflection. This means that the radius of the disc used for accomplishing high density recording in this prior art example is about 10 mm.
As described above, whereas the fineness of the electron beam has been stressed and the attempt has been made to improve the density of the recording device, the increase in the recording capacity has been rather neglected.